Autopilot monitor system



June 14, 1960 H. w. PATTON 2,941,193

AuToPILoT MONITOR SYSTEM Filed July 1s, 195e 9 ,N E s a@ m q s IllulEllhll-uwll l o 's 2 5l r si D q BIL E Q b *z i9 'n q III| u o &

f u) E g Ll INVENTOR.

S HENRY W PnTroN www@ A Tro RNsvs AUTOPILO'I MONTIOR SYSTEM Henry W.Patton, Cedar Rapids, Iowa, assignor to Collins Radio Company, CedarRapids, Iowa, a corporation of Iowa Y v Filed July 16, 1956, Ser. No.597,955

This invention relates to alarm circuits, and more particularly to anelectronic alarm circuit for adaptation with automatic pilot systems.

This current produces a directional torque with the greater' torquebeing applied to the capstan by the clutch with the greater currentflowing through it. In an aircraft automatic pilot system a malfunctionin the control unit or in the operation of these clutches can result intragic consequences to the aircraft. This invention provides an alarmcircuit which will indicatev malfunctioning in the circuit used tocontrol the capstan, yet be'rclatively in sensitive to normalmaneuvering.

This invention provides an alarm circuit which will be actuated vwhenthe current flowing in'one of the two clutches is of a predeterminedvalue for a specified time interval. This current may be in onedirection only,l due to a large sustained signal, or it may result froma sustained differential signal, causing differences in the currents inthe related clutches. These current differences cause the alarm systemof this invention to operate. n

' This invention also provides for normal increase in the averagecurrent iiow through the clutches, which occurs when there is anincrease in the roughness of the weather.

This invention also provides for large momentary command signals whichwill cause large currents to ow momentarily but will not necessarily ofthemselves operate the alarm circuit. The alarm circuit of thisinvention will operate only with a large and relatively prolongedcommand voltage or current being applied in a single direction.

It is a feature of this invention that the currents flowing through theclutch coils determine the functioning of the alarm circuit. It is afurther feature of this invention that only true malfunctioning of theautomatic pilot system will operate the alarm circuit, while full clutchcurrents of a transient nature will not actuate the alarm.

It is an object of this invention to provide an alarm circuit for use inan automatic pilot system which will be responsive to malfunctionings ofthe automatic pilot system. It is a further object of this invention toprovide an alarm circuit where the currents in two clutches are comparedand where only a predetermined differential effect for a predeterminedlength of time will operate the alarm circuit. It is a still furtherobject of this invention to provide an alarm circuit which does notrespond to the current flow in the clutch coils caused by strong orlarge command signals when these signals are of normal The control forUnited States Patent 2,941,193 Patented June 14, 1960 ICC duration. Itis another object of this invention to-provide an economical alarmcircuit for use with automatic pilot systems which may be combined topermit independent operation of any single axis alarm withoutinterfering with the alarms and operations associated with the remainingaxes.

These and other objects of this invention will becomel apparent when thefollowing description is read in con-- junction with the drawings, inwhich Figure 1 is a schematic diagram of one embodiment of thisinvention;

Figure 2'is a schematic diagram of this invention 'as'. applied toaithree-axis control system; and

Figure 3 is a view of one embodiment of a clutch. mechanism and gearingused to control the rotation of.' the capstan.

Referring now to Figure 3, the continuously running motor 8 turns. thegears connected to the clutches 7. The currents flowing through thecoils in the clutches 7 deter# mine the direction of rotation and thevelocity of rota-- tion of the gear 9. Gear 9 then rotates capstan 10in. conformity with the signals from the clutches 7. Rotation of thecapstan 10 provides the final mechanical control signals which aredelivered to the various airplane controls, such as the elevator,aileron, and rudder.

Figure l is a detailed schematic of one embodiment of' this invention.The control signals are generated and fed to amplifier 5 as inputsignals. These input signals are amplified in amplifier 5 and thenapplied to the coils 6. of the clutches 7. The signals fed to the clutchcoils. will cause a current to fiow in one of the coils 6 throughA onehalf of the filament of tube 11 to ground. Tube 11" is depicted as adouble diode which may be replaced by two individual diodes. If anexcessively large amount of current flows through either of the clutchcoils 6 for an extended period of time, one half of the filament of tube11 will heat to the' emissive point and will cause conduction in thishalf of the tube. Whenever conduction occurs on either side of tube 11,a current ilows through the coil 4 of neutral center differential relay12. This current will actually flow through one half of coil 4 of therelay 12 for each clutch action, i.e., right or left or uptor down. Thecurrent results from the application of the alternating current voltagefrom source 18 to the plate circuit of tube 11 which may includegas-filled tubes 16 and parallel connected resistors 17. When adifferential or net magnetic pull is created by currents flowing ineither side of relay 12, the contact arm will close the contacts 13thereby initiating an alarm. The contacts and contact arm are designatedby the numeral 13 in Figure l. The swinging of the contact arm willoperate the alarm through the indicator 14 from the power source 15.

During normal fiight in smooth air the clutch currents ilowing throughthe filament halves are approximately equal and are normally small.Consequently, there is little or no heating of the filament and littletube conduction occurs which would cause operation of the alarmcircuitry. In rough air, false operation of the alarm circuit isprevented by the combination of the inverse thermal time delay action ofthe tube filaments and the differential action of relay 12. While largeraverage clutch command signals will cause greater current ow through thefilament halves, the heating eifect averaged over several seconds tendsto equalize. This equalization means that the same heating occurs inboth filaments, which results in equal plate currents through the tubehalves. With equal plate currents through the tube halves nodifferential action of coil 4 of relay 12 will occur, and undesiredtripping of the alarm is prevented.

Figure 2 indicates a system for connecting a combina- Ytion of vthree ofthe control circuits of this invention together with one alarmindicator, and applying them to a single three-axis automatic pilotsystem. The clutch signals are `applied -to and Aoperate on c ach of thetubes 2,1, 22;, and I23yexac't'ly as they operated on tube `11 in theabove description. One voi the tubes, 21, is rudder controlled; Aanothertube, 22, is for the aileron 'control circuit; and the lastY tube, 23,is for the elevator control circuit. It is to be noted that 'the alarmcircuit is con nected to the cathodes of all three tubes so 'that- Yonealarm circuit may show faults in any of the chosen command circuits. i fThe .gaseous tubes 16 are optional,` and are used in the plate circuitsof the tubes Il paralleled by the load resistors 17' to .provide quickor snap action when 'the current flow iti/)the .plate circuit attainsacerta-in fvalue of..potential. This results ina sudden increaseof-cirrents inthe -cathode circuit due to the conduction of the tubes vI1. This increase in current flow beyond the danger point reduces thehesitation and false operation of diifer'eritial relay n1-2.VThus,lwh`en the command signal is clearly erroneous, the ionization oftube 16 permits the quick soundingk of the alarm circuit of thisinvention.

Although this Ainvention has been described with respec't to `aparticular embodiment thereof, it is not to be so. limited, as changesand -modiiications may be -m-ade therein which are within the fullIintended scope ofthe invention as defined by the appended claims.

What is claimed is: l I ur l. ln an aircraft autopilot system of thetype including directional control signals, anY amplifier for-amplifyingsaidcont'rol signals and clutch means including clutch driving coils andmonitor means for controlling the ontput from `a drive motor whichpositions the night surfaces of 'said-aircraft in response to saidcontrol signals; a^rnalfunetionrnonitoring system comprising electrondischarge means including. at least two plates, two cathodes and twoheater elements, each of saidV clutch driving coils individuallyserially connected through one of said heater elements to said controlsignals, a differential current-sensing means, said cathodes connectedto opposite ends of said differential current-sensing means, a source ofelectromotive force vhaving one side connected to said plates andtheother side connected to thev center of said current-sensing means,lswitch meansl responsive to differential current fl'o'w in saiddifferential current-sensing means, an kalarrnfdevice and a: source of,power connected to said alarm device by. said switching means when adifferential current flows 1in said differential current-sensing means.r2. In an aircraft autopilot system of the type including directionalcontrol signals, an amplifier for amplifying said control signals, andclutch means including clutch driving coils and monitor means forcontrolling the output from a drive motor which positions the flightsurfaces of said aircraft in response to said control signals; amalfunction monitoring system comprising an electron discharge devicehaving at least two plates, two cathodes and two heater elements, saiddriving coils individually serially connected through said heaterelements to said control signals, a differential current-sensing meanscomprising a center-tapped coil, said cathodes Vconnected to oppositeends of said differential current-'sensing means, a source ofelectromotive force having one vside'co'rir'ie'iited to said plates andthe other side connected to' the center tap of `said coil, lswitcl1means responsive to differential current flow in said differentialentrent-sensing means, an alarm device and a source of power connectedto said alarm device by said switching means for providing warningsignalsA when 5a Vdifferential current flows `in -said differentialcurrent-'sensing means sufficient of value' to ac tuate said switchmeans.

V3. vInan aircraft autopilot system of the type including directionalvcontrol signals, Aan amplier Afor amplifying said control signals,-fand clutch means including Vclutch driving coils and monitor means forcontrolling the outputffrom a motor means which controls the flight ofsaid aircraft in 'response to said control signals; a malfunctionmonitoring system comprising an electron discharge'edev-ice having atleast two plates', two cathodes ,and two heater elements, said clutchdriving -coi-ls individually serially connected through said heaterelements to `said control signais, a differential current-sensing meansconn prising a center-tapped coil, said cathodes connected to oppositeends of said differential current-sensing means, fa source of.`electomotiv'e force having one side connected to Yeaeh"of1saicl.pla-tes through identical circuits comprising Ya-resistarnze and afgaslled electron discharge device connected in parallel,` switch meansresponsive to apre` determined value of differential current -ow Yinsaid differential current-sensing means, an alarm devicel anda source ofpower connected toy saidV alarm device by `said switch-ing meansforpi'oviding warning signals when'l a prescribed' 'differential currentis owing in said: differential current=sensing means'.

References Cited in the -file of this .patent ''tni STATES PATENTS

